/**
\defgroup quickref Function quick reference
@{

\section sensors Sensor functions

Some sensors generate events when the sensors change. It is always
possible to query the state of a sensor through a set of query functions.

\subsection quickref-sensors-events Sensor events

- \ref sensors_event_button_down - the button has been pressed
- \ref sensors_event_button_up - the button has been depressed
- \ref sensors_event_humidity - a change in humidity has been detected
- \ref sensors_event_light - a change in light has been detected
- \ref sensors_event_motion - motion has been detected
- \ref sensors_event_sound - sound has been detected
- \ref sensors_event_temperature - temperature has changed
- \ref sensors_event_vibration - vibration has been detected

\subsection quickref-sensors-query Sensor query functions

- sensors_battery() - query the battery voltage level
- sensors_button() - query the on-board button
- sensors_mic() - query the microphone
- sensors_pir() - query the passive IR sensor (motion detector)
- sensors_radiosignal() - query the radio signal strength
- sensors_temp() - query the temperature sensor
- sensors_vib() - query the vibration sensor

\section quickref-leds LED functions

- leds_on() - turn LEDs on
- leds_off() - turn LEDs off
- leds_invert() - invert LEDs
- leds_blink() - blink all LEDs

\section quickref-beeper Beeper functions

- beep() - click the beeper
- beep_beep() - beep
- beep_down() - pitchbend down beep
- beep_quick() - a number of quick beeps
- beep_spinup() - pitchbend up beep

\section quickref-timers Timer functions

Contiki supports two types of timers: event timers and simple
timers. Event timers generates an event when the timer expires,
whereas the simple timer has to be actively queried to check when it
has expired.

\subsection quickref-etimer Event timers

- etimer_expired() - check if an event timer has expired
- etimer_set() - set an event timer
- etimer_reset() - set an expired event timer to the next interval
- etimer_restart() - restart an event timer from the current point in time

\subsection quickref-timer Simple timers

- timer_expired() - check if a simple timer has expired
- timer_set() - set a simple timer
- timer_reset() - set a simple event timer to the next interval
- timer_restart() - restart a simple timer from the current point in time


*//** @{ */